The present invention relates in general to regulating the intensity of light emitted by a lamp and more particularly concerns light dimming circuits having variable inductors.
Light dimming circuits can provide substantial energy savings by permitting a user to reduce light intensity to a desired level or by permitting automatic regulation of light intensity based on, e.g., the time of day or input from a motion detector that detects the presence of a person in a room.
Light dimming circuits for fluorescent lamps and the like are known in which light intensity is varied by adjusting the inductance of a variable inductor. Examples of such circuits are disclosed in U.S. Pat. No. 5,140,228 filed Feb. 23, 1990, the entire disclosure of which is incorporated herein by reference. In particular, the above-mentioned U.S. application discloses a variable inductor connected in parallel with a fluorescent lamp powered by a high-frequency alternating current. Other light dimming circuits for fluorescent lamps powered at lower frequencies include a variable inductor connected in series with the lamp.
The inductance of the variable inductor disclosed in the above-mentioned U.S. application is varied by adjusting the geometry of the ferrite core around which the inductor is wrapped.